Optical fibers are often used to transmit electromagnetic signals. As a result of the geometry of such fibers, each fiber is typically configured to guide electromagnetic waves within only a limited range of wavelengths. In situations in which electromagnetic signals having significantly different wavelengths (e.g., signals from opposite ends of the electromagnetic spectrum) are to be transmitted, multiple fibers are typically required, one for each wavelength. The need for multiple fibers increases the complexity of the systems in which the fibers are used. It would therefore be desirable to have optical fibers or other waveguides that can transmit both relatively short and relatively long wavelength electromagnetic signals.